Generator arrangement

ABSTRACT

A generator arrangement comprises a turbocharger having a compressor configured to be placed in fluid flow communication with an engine inlet, and a first turbine having a first turbine wheel, a first inducer portion upstream, in use, of the first turbine wheel and configured to be placed in fluid flow communication with an engine outlet, and a first exducer portion downstream, in use, of the first turbine wheel; and an electrical generator having a second turbine having a second turbine wheel, a second inducer portion upstream, in use, of the second turbine wheel and configured to be placed in fluid flow communication with the engine outlet, and a second exducer portion downstream, in use, of the second turbine wheel. The first and second turbines are arranged in parallel to one another; and the first inducer portion and second inducer portion, and/or the first exducer portion and second exducer portion are contiguous.

The present invention relates to a generator arrangement. In particular, the present invention relates to a generator arrangement having a turbocharger and a power turbine.

Turbochargers are well known devices for supplying air to an inlet of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to an engine inlet manifold. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housings.

The turbine stage of a typical turbocharger comprises: a turbine chamber within which the turbine wheel is mounted; an annular inlet defined between facing radial walls arranged around the turbine chamber; an inlet volute arranged around the annular inlet; and an outlet passageway extending from the turbine chamber. The passageways and chamber communicate such that pressurised exhaust gas admitted to the inlet volute flows through the inlet to the outlet passageway via the turbine chamber and rotates the turbine wheel. It is also known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet so as to deflect gas flowing through the inlet. That is, gas flowing through the annular inlet flows through inlet passages (defined between adjacent vanes) which induce swirl in the gas flow, turning the flow direction towards the direction of rotation of the turbine wheel.

Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that characteristics of the inlet (such as the inlets size) can be varied to optimise gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suit varying engine demands. For instance, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the inlet using a variable geometry mechanism. Turbochargers provided with a variable geometry turbine are referred to as variable geometry turbochargers.

Nozzle vane arrangements in variable geometry turbochargers can take different forms. Two known types of variable geometry turbine are swing vane turbochargers and sliding nozzle turbochargers.

Generally, in swing vane turbochargers the inlet size (or flow size) of a turbocharger turbine is controlled by an array of movable vanes in the turbine inlet. Each vane can pivot about an axis extending across the inlet parallel to the turbocharger shaft and aligned with a point approximately half way along the vane length. A vane actuating mechanism is provided which is linked to each of the vanes and is displaceable in a manner which causes each of the vanes to move in unison, such a movement enabling the cross sectional area available for the incoming gas and the angle of approach of the gas to the turbine wheel to be controlled.

Generally, in sliding nozzle turbochargers the vanes are fixed to an axially movable wall that slides across the inlet. The axially movable wall moves towards a facing shroud plate in order to close down the inlet and in so doing the vanes pass through apertures in the shroud plate. Alternatively, the nozzle ring is fixed to a wall of the turbine and a shroud plate is moved over the vanes to vary the size of the inlet.

A known type of engine is a hybrid electric engine. A hybrid electric vehicle is a vehicle which has a powertrain that includes a hybrid electric engine (which may combine a conventional internal combustion engine propulsion system and an electric propulsion system). The presence of the electric propulsion system as part of the powertrain is intended to achieve improved fuel economy or improved performance compared to a conventional vehicle (i.e. a vehicle which has a internal combustion engine propulsion system only).

The internal combustion engine portion of a hybrid electric engine usually produces less emissions compared to a standard internal combustion engine which has a comparable power output to the hybrid electric engine. This may be because the internal combustion engine portion of a hybrid electric engine is generally smaller than a standard internal combustion engine which has a comparable power output to the hybrid electric engine.

Some known hybrid electric vehicles use a hybrid electric engine in which the internal combustion engine generates electricity by powering an electrical generator to either directly power electric drive motors or to recharge batteries.

A known method by which an internal combustion engine can be used to generate electricity by powering an electrical generator, is to use a power turbine. The power turbine may comprise an exhaust gas driven turbine wheel mounted on a rotatable shaft which drives the electrical generator.

The exhaust driven turbine wheel of the power turbine may be driven so fast that the attached electrical generator cannot effectively generate electricity, due to operational limitations of the electrical generator. For this reason, some power turbines may include gearing between the turbine wheel and the electrical generator to reduce the speed at which the electrical generator is driven by the turbine wheel to within the operational limitations of the electrical generator. However, such gearing may be complex, costly and prone to failure.

A known generator arrangement may have an exhaust gas driven power turbine and a turbocharger. The power turbine and turbine of the turbocharger may be connected downstream of an outlet of an engine in series such that exhaust gas from the engine outlet passes through the turbine of the turbocharger and then through the power turbine. This type of generator arrangement may be referred to as a series generator arrangement.

Series generator arrangements may be large and heavy due to the fact that the relatively low pressure experienced by the downstream power turbine necessitates that the power turbine is relatively large. Large and heavy series generator arrangements may be expensive due to the fact that they are constructed from more material than relatively smaller generator arrangements. Furthermore, large and heavy generator arrangements may be unsuitable for use in applications where space and/or maximum possible weight is limited.

Known generator arrangements may be constructed from many separate parts which increases the complexity and assembly time of such generator arrangements. Known generator arrangements which have an increased assembly time may be more costly to produce.

It is an object of the present invention to provide a generator arrangement which obviates or mitigates at least one of the above described disadvantages or disadvantages present in the prior art. It is another object of the present invention to provide an alternative generator arrangement.

According to a first aspect of the present invention there is provided a generator arrangement comprising a turbocharger having a compressor configured to be placed in fluid flow communication with an engine inlet, and a first turbine having a first turbine wheel, a first inducer portion upstream, in use, of the first turbine wheel and configured to be placed in fluid flow communication with an engine outlet, and a first exducer portion downstream, in use, of the first turbine wheel; and an electrical generator having a second turbine having a second turbine wheel, a second inducer portion upstream, in use, of the second turbine wheel and configured to be placed in fluid flow communication with the engine outlet, and a second exducer portion downstream, in use, of the second turbine wheel; wherein the first and second turbines are arranged in parallel to one another; and wherein the first inducer portion and second inducer portion, and/or the first exducer portion and second exducer portion are contiguous.

The generator arrangement may comprise a housing which defines at least a portion of a first turbine housing of the first turbine and at least portion of a second turbine housing of the second turbine, wherein the portion of the of the first turbine housing defines at least part of the first exducer portion, at least part of the first inducer portion or at least part of a first turbine chamber within which the first turbine wheel is located, and wherein the portion of the of the second turbine housing defines at least part of the second exducer portion, at least part the second inducer portion or at least part of a second turbine chamber within which the second turbine wheel is located.

The housing may be of unitary construction.

The second turbine may be a radial inflow turbine.

The first turbine and/or second turbine may be variable geometry turbines.

The second turbine may comprise a flow control device which is configured to control the flow of fluid from the engine outlet to the second turbine.

The flow control device may be a valve.

The first turbine wheel may, in use, rotate about a first axis, and the second turbine wheel, in use, may rotate about a second axis, the first and second axes being substantially parallel.

The first inducer portion may comprise an inducer port to which the second inducer portion is connected, and/or wherein the first exducer portion comprises a exducer port to which the second exducer portion is connected.

The first inducer portion may comprise an inducer port to which the second inducer portion is connected, and wherein, in use, the angle subtended between the general flow direction of fluid within a portion of the first inducer portion upstream of the inducer port and the general flow direction of fluid within a portion of the second inducer portion downstream of the inducer port is less than about 90 degrees. In some embodiments the angle subtended between the general flow direction of fluid within a portion of the first inducer portion upstream of the inducer port and the general flow direction of fluid within a portion of the second inducer portion downstream of the inducer port may be less than at least one of about 60 degrees, 45 degrees, 30 degrees, 15 degrees, 10 degrees and/or 5 degrees.

The first exducer portion may comprise an exducer port to which the second exducer portion is connected, and wherein, in use, the angle subtended between the general flow direction of fluid within a portion of the second exducer portion upstream of the exducer port and the general flow direction of fluid within a portion of the first exducer portion downstream of the exducer port is less than about 90 degrees. In some embodiments the angle subtended between the general flow direction of fluid within a portion of the second exducer portion upstream of the exducer port and the general flow direction of fluid within a portion of the first exducer portion downstream of the exducer port may be less than at least one of about 60 degrees, 45 degrees, 30 degrees, 15 degrees, 10 degrees and/or 5 degrees.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing the layout of a known generator arrangement;

FIG. 2 is a schematic diagram showing the layout of a generator arrangement in accordance with a first embodiment of the present invention;

FIG. 3 is a schematic diagram showing the layout of a generator arrangement in accordance with a second embodiment of the present invention;

FIG. 4 is a schematic cross-section through a generator and a portion of a turbine of a turbocharger which form part of a generator arrangement in accordance with an embodiment of the present invention;

FIG. 5 is a schematic side view of a turbine of a generator and a turbine of a turbocharger which form part of a generator arrangement in accordance with an embodiment of the present invention;

FIG. 6 is a schematic side view of a turbine of a generator and a turbine of a turbocharger which form part of a generator arrangement in accordance with another embodiment of the present invention; and

FIG. 7 is a schematic side view of a turbine of a generator and a turbine of a turbocharger which form part of a generator arrangement in accordance with a further embodiment of the present invention.

FIG. 1 shows a known generator arrangement 10. The generator arrangement is linked to an engine 12 and includes an associated turbocharger 14. The turbocharger 14 has a compressor having a compressor wheel (not shown) and a turbine 18 having a turbine wheel (also not shown). The compressor wheel and turbine wheel are linked by a rotatable shaft 20.

The engine 12 has an engine exhaust outlet 22. An inlet to the turbine 18 of the turbocharger 14 is connected to the engine outlet 22 such that the turbine 18 is in fluid flow communication with the engine outlet 22. Exhaust gases produced by the engine 12 are provided to the turbine 18 via the engine outlet 22 and cause the turbine wheel within the turbine 18 to rotate. Rotation of the turbine wheel, and hence the attached shaft 20, results in the rotation of the compressor wheel within the compressor 16.

The compressor 16 is connected to an engine inlet 24 in a manner such that the compressor 16 is in fluid flow communication with the engine inlet 24. The compressor 16 is also connected to a fluid source 26. In this case, the fluid concerned is a gas, and more particularly, is air. The fluid source 26 in this case is the atmosphere.

As previously discussed, the compressor wheel within the compressor 16 is rotated via the shaft 20 due to the rotation of the turbine wheel within the turbine 18 caused by the passage of exhaust gas through the turbine 18. Rotation of the compressor wheel within the compressor 16 results in the compressor 16 supplying fluid from the fluid source 26 to the engine 12 via the engine inlet 24. The pressure of the fluid supplied to the engine inlet 24 by the compressor 16 is at a higher pressure (also known as boost pressure) compared to that of the fluid at the fluid source 26.

The turbine 18 has an outlet 28 to which exhaust gas passes once it has passed through the turbine 18 from the engine outlet 22.

The generator arrangement 10 also has an electrical generator 30. The electrical generator 30 comprises a turbine 32 having a turbine wheel (not shown). The turbine wheel is linked via a shaft 34 to a transducer 36. In this case, the transducer 36 is an electric generator. The transducer 36 operates such that rotation of the turbine wheel of the turbine 32 causes rotation of the shaft 34, and the transducer 36 converts at least part of energy of the rotary motion of the shaft 34 into electrical power. Exhaust gas that is provided to the turbine 32 via the turbine outlet 28 from the turbine 18 causes the turbine wheel within the turbine 32 to rotate and hence the generator 30 generates electrical power.

The turbine 32 of the generator 30 is connected to the turbine outlet 28 such that the turbine outlet 28 and turbine 32 are in fluid flow communication with one another.

Exhaust gas from the engine 12 which passes through the turbine 18 of the turbocharger and then passes to the turbine 32 of the generator and hence rotates the turbine wheel within the turbine 32. This causes the transducer 36 of the generator 30 to produce electrical power. The electrical power may then be stored (for example, using batteries) or utilised in any other appropriate manner as would be appreciated by the person skilled in the art.

Due to the fact that the inlet of the turbine 32 of the generator 30 is in fluid flow communication with the outlet of the turbine 18 of the turbocharger 14, such that the turbine 32 of the generator 30 is downstream of the turbine 18 of the turbocharger 14, the turbocharger 14 and generator (or power turbine) 30 may be said to be arranged in series.

The turbine 18 of the turbocharger 14 within the generator arrangement 10 is provided with a wastegate valve indicated generally by 38. The wastegate valve 38 can be used to define a flow path which can be selectively opened or closed and which allows exhaust gas produced by the engine to substantially bypass the turbine 18 of the turbocharger 14. When the wastegate valve 38 is open exhaust gas may flow from the engine outlet 22 to the turbine outlet 28 such that substantially less exhaust gas passes the turbine wheel in the turbine 18 compared to when the wastegate valve 38 is closed. In some embodiments, substantially no exhaust gas may pass the turbine wheel within the turbine 18 when the wastegate valve 38 is open.

It will be appreciated that by opening the wastegate valve 38 (and therefore reducing the amount of exhaust gas which passes from the engine 12 to the turbine wheel of the turbine 18) the force exerted on the turbine wheel of the turbine by exhaust gases from the engine is reduced. This results in a reduction in the speed of rotation of the turbine wheel, and hence a reduction in the speed of rotation of the compressor wheel (caused by the rotation of the turbine wheel). This reduction in the speed of rotation of the compressor wheel of the compressor 16 results in a reduction in the rate at which fluid which is transferred to the engine by the compressor 16 via the engine inlet 24.

Furthermore, opening the wastegate valve 38, by allowing the exhaust gas produced by the engine 12 to bypass the turbine 18 of the turbocharger 14 and therefore to pass directly to the turbine 32 of the generator 30 will increase the proportion of the energy of the exhaust gas which is passed to the turbine 32 of the generator 30 and therefore converted to electrical power by the transducer 36.

One disadvantage of this generator arrangement is that the size of the turbine wheels within the turbocharger 14 and generator 30 have to be relatively large to accommodate a full flow of the exhaust gas given the partial pressure ratio of such turbines. Such relatively large turbine wheels may be costly to produce. Furthermore, there is limited control over the operation of the generator arrangement in conjunction with the operating condition of the engine 12. For example, it is only possible to control how much exhaust gas is allowed to bypass the turbine 18 of the turbocharger and hence how much exhaust gas passes to the turbine 32 of the generator 30 without passing through the turbine 18 of the turbocharger 14.

FIG. 2 shows a schematic diagram of a generator arrangement 40 in accordance with a first embodiment of the present invention. The generator arrangement 40 is attached to an engine 42 having an engine inlet 44 and an engine outlet 46. The engine inlet 44 and engine outlet 46 may be referred to as the engine inlet manifold and the engine outlet manifold respectively. The generator arrangement further comprises a variable geometry turbocharger 48 and a generator 50.

The generator arrangement 40 includes a variable geometry turbocharger 48. The variable geometry turbocharger 48 comprises a compressor 52 housing a compressor wheel (not shown), and a variable geometry turbine 54 housing a turbine wheel (not shown). The turbine wheel and compressor wheel are linked by an intermediate shaft 56.

The compressor 52 of the variable geometry turbine has an inlet 58 and an outlet 60. The outlet 60 of the compressor 52 is arranged such that it is in fluid flow communication with the engine inlet 44. The inlet 58 of the compressor 52 is arranged such that it is in fluid flow communication with a gas source 62. In this case, the gas is air and the gas source 62 is the atmosphere.

Although in this embodiment of the present invention (and in all further embodiments of the invention discussed below) the fluid source is a gas source (i.e. the atmosphere) in fluid flow communication with the inlet of the compressor of the turbocharger, it will be appreciated that in other embodiments of the invention the gas source may be replaced by another fluid source. For example the fluid source may be a liquid source. Alternatively, a gas source other than the atmosphere, may be used. Alternatively, a gas other than air, and a source of gas other than a source of air may be used.

The variable geometry turbine 54 of the turbocharger 48 has an inlet 64 and an outlet 66. The inlet 64 of the turbine 54 is arranged such that it is in fluid flow communication with the engine outlet 46. The outlet 66 of the turbine 54 is arranged such that it is in fluid flow communication with an arrangement outlet 68.

Due to the fact that the turbine of the turbocharger 48 is a variable geometry turbine, the size of the inlet 64 can be varied using a variable geometry mechanism (not shown) so as to optimise the flow velocity of gas flowing through the inlet over a range of mass flow rates of the engine exhaust gas. This enables the power outlet of the turbine 54 to be varied to suit different engine operating conditions. For example, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel can be maintained at a level which ensures efficient turbine operation by reducing the size of the inlet using the variable geometry mechanism. Two known types of variable geometry turbine are swing vane turbines and sliding nozzle turbines. The structure and operation of such turbines is well known to those skilled in the art.

The generator 50 comprises a variable geometry turbine 70 housing a turbine wheel (not shown) which is linked via a shaft 72 to a transducer 74.

The transducer 74 is configured such that it can convert rotation of the shaft 72 into a desired form of power. For example, the transducer may convert the rotation of the shaft 72 into different motion. However, in this case, the transducer 74 converts rotation of the shaft 72 into electrical power. For this reason, the transducer 74 may be referred to as an electric generator.

A turbine which is connected to a transducer such that the transducer converts the rotation of the turbine wheel within the turbine into another type of power may be referred to as a power turbine.

The turbine 70 of the generator 50 is a variable geometry turbine and has a variable geometry inlet 76 and an outlet 78. The turbine 70 may be arranged such that the flow of the exhaust gas into the turbine 70 via the inlet 76 is substantially perpendicular to the axis about which the generator shaft 76 rotates. It follows that the turbine 70 may be referred to as a radial-inflow turbine.

The outlet 78 of the turbine 70 is arranged such that it is in fluid flow communication with the arrangement outlet 68. The inlet 76 of the turbine 70 is arranged such that it is in fluid flow communication with the engine outlet 46.

Due to the fact that the inlet 64 of the turbine 54 of the turbocharger 48 and the inlet 76 of the turbine 70 of the generator 50 are both in fluid flow communication with the engine outlet 46, the turbocharger 48 and generator (or power turbine) 50 may be said to be arranged in parallel. Although the turbocharger 48 and generator 50 arranged in parallel in this embodiment both have inlets which are in fluid flow communication with the engine outlet, in other embodiments, this need not be the case. For example, in some embodiments, the turbocharger 48 and generator 50 may be arranged in parallel such that both have inlets which are in fluid flow communication with any appropriate common outlet.

It will be appreciated that, although the inlet 64 of the turbine 54 and the inlet 76 of the turbine 70 are both connected so that they are in fluid flow communication with a single engine outlet 46, this need not be the case in some embodiments of the present invention. For example, the inlet 64 of the turbine 54 of the turbocharger 48 may be connected such that it is in fluid flow communication with a first engine outlet, whereas the inlet 76 of the turbine 70 of the generator 50 may be connected such that it is in fluid flow communication with a second engine outlet. For example, the first engine outlet may be linked to a first exhaust manifold which receives exhaust from a first set of engine cylinders, whereas the second engine outlet may be linked to a second exhaust manifold which has exhaust provided to it by a second set of engine cylinders. This arrangement, whereby the inlet of the turbine of the turbocharger is connected such that it is in fluid flow communication with a first engine outlet, and whereby the inlet to the turbine of the generator is connected such that it is in fluid flow communication with a second exhaust outlet of the engine may also be applied any of the embodiments of the invention discussed below.

Within the embodiment of the invention shown in FIG. 2, the outlet 66 of the turbine 54 of the turbocharger 48 and the outlet 78 of the turbine of the generator 50 are both in fluid flow communication with the arrangement outlet 68. This need not be the case in other embodiments of the invention. For example, in some embodiments, the outlet of the turbine of the turbocharger, and the outlet of the turbine of the generator may be in fluid flow communication with separate outlets. This applies equally to other embodiments of the invention discussed below.

The generator arrangement shown in FIG. 2 operates as follows. When the engine 42 is operating it produces exhaust gas which is supplied to the engine exhaust outlet 46. The exhaust gas then flows from the engine exhaust outlet 46 to both the inlet of the turbine of the turbocharger 48 and the inlet 76 of the turbine 70 of the generator 50.

In relation to the turbine 54 of the turbocharger 48, the exhaust gas passes from the turbine inlet 64 via a variable geometry mechanism (not shown) into the turbine 54 and past a turbine wheel (not shown). As the exhaust gas passes the turbine wheel it imparts a force to the turbine wheel and hence causes the turbine wheel to rotate. The exhaust gas then flows out of the turbine 54 via the turbine outlet 66 to the arrangement outlet 68.

In relation to the turbine 70 of the generator 50, the exhaust gas passes from the turbine inlet 76 into the turbine 70 and via variable geometry mechanism (not shown) such that the exhaust gas passes the turbine wheel (not shown) of the turbine 70. As the exhaust gas passes the turbine wheel it exerts a force on the turbine wheel thereby causing the turbine wheel to rotate. Once the exhaust gas has flowed past the turbine wheel of the turbine 70 it flows out of the turbine 70 via the turbine outlet 78 and into the arrangement outlet 68.

In the case of the generator 50, rotation of the turbine wheel within the turbine 70 causes rotational movement to be transmitted to the transducer 74 (an electric generator in this case) via the shaft 72. The transducer 74 produces a power output (in this case electrical power). The power generated by the transducer 74 may then be stored (for example by batteries) or utilised to power another device. For example, if the generator arrangement is utilised as part of a hybrid electric engine, the transducer 74 may produce electric power which is supplied to the electric propulsion system. The electric power supplied to the electric propulsion system may power a motor.

In relation to the turbocharger 48, rotation of the turbine wheel of the turbine 54 by the exhaust gas results in the compressor wheel within the compressor 52 being rotated via the shaft 56. Rotation of the compressor wheel within the compressor 52 causes the compressor to draw gas (air in this case) from the gas source 62 into the compressor 52 via the inlet 58. The air then passes the compressor wheel within the compressor 52 and is urged by the compressor in an upstream direction to the engine inlet 44 via the compressor outlet 60.

As previously discussed, within the generator arrangement shown in FIG. 2, the arrangement of the turbines 54 and 70 of the turbocharger 48 and generator 50 such that their respective inlets 64 and 76 are both connected to the engine outlet 46 (or in other embodiments separate engine outlets) means that the turbocharger 48 and generator 50 can be said to be arranged in parallel to one another.

The arrangement of the turbocharger 48 and generator 50 in parallel (as opposed to the series arrangement of the known turbocharger and generator arrangement shown in FIG. 1) is beneficial for several reasons.

Due to the fact that the turbine of the generator of the parallel arrangement is connected to the engine outlet 46, as opposed to being downstream of the turbocharger in the series arrangement shown in FIG. 1, the turbine 70 of the generator 50 is exposed to the full pressure ratio of exhaust gas produced by the engine 42. By exposing the turbine 70 of the generator 50 to the full pressure ratio of exhaust gas, the size of the turbine 70 can be reduced compared to the required size of turbine in a series arrangement. This is because the power output by the turbine is a function of the pressure of the gas supplied to the turbine (and hence the pressure ratio of the exhaust gas) and of the size of the turbine wheel of the turbine. By increasing the pressure ratio (and hence the pressure) of gas supplied to the turbine, the size of the turbine wheel of the turbine can be reduced without reducing the power produced by the turbine. A reduction in the size of the turbine wheel means that less material is required in order to manufacture the turbine wheel and hence the cost of producing the turbine wheel is reduced.

Another effect of reducing the size of the turbine wheel is that the transient response of the turbocharger of which the turbine forms part is improved. That is to say that the time required to rotate the turbine wheel (and hence the compressor wheel) up to a speed at which the turbocharger can effectively supply air to the engine at boost pressure is reduced. This time may also be referred to as turbo lag. Turbo lag is reduced by reducing the size of the turbine wheel because reducing the size of the turbine wheel reduces its moment of inertia and hence reduces the torque required to accelerate the turbine wheel (and attached compressor wheel) to a given rotational speed. Hence, reducing the size of the turbine wheel reduces turbo lag and hence improves the performance of the turbocharger and the engine to which the turbocharger is attached.

A further effect of reducing the size of the turbine wheel of the turbine 70 of the generator 50 is that, for a given mass flow rate and pressure of gas provided to the turbine 70, the speed at which the turbine wheel (and hence the attached shaft 72 supplying the transducer 74) will rotate is increased.

Previous known electrical generators have not been capable of operating at the high rotational speeds which are achieved by the smaller sized turbine wheel of the generator. However, certain transducers, such as recently developed and future planned electrical generators, may operate at the high speed of rotation achieved by the smaller sized turbine wheel of the generator. Operating the transducer at a higher speed of rotation may be beneficial. For example, certain transducers may produce more power output when they are rotated at a greater speed. For example, certain electrical generators may produce more electrical power when they are rotated at a greater speed. Hence, in the case of transducers which are suited to the greater rotational speeds (such as certain electrical generators) produced by the smaller turbine wheel of the generator turbine, it has been found that there is a synergistic effect provided by the generator arrangement according to the present invention whereby a smaller turbine may be used as part of the generator which both reduces the cost of the turbine and increases the power which can be produced by the transducer of the generator.

The generator arrangement according to the present invention shown in FIG. 2 comprises two flow control mechanisms which each control the flow of exhaust gas through a portion of the generator arrangement. The variable geometry mechanism of the turbine 54 of the turbocharger 48 is a first flow control mechanism. The first flow control mechanism (in this case the variable geometry mechanism of the turbine 54) is configured to control the flow of exhaust gas from the engine outlet 46 to the turbine 54. The variable geometry mechanism of the turbine 70 of the generator 50 constitutes a second flow control mechanism. The second flow control mechanism is configured to control the flow of exhaust gas from the engine outlet 46 to the turbine 70. In contrast to the generator arrangements of the present invention, the known generator arrangement shown in FIG. 1 has only a single flow control mechanism. In this case the flow control mechanism is the wastegate 38. The wastegate 38 controls the flow of exhaust gas to the turbine of the turbocharger of the known generator arrangement by allowing exhaust gas to selectively bypass the turbine of the turbocharger.

A person skilled in the art may not seek to add a second flow control mechanism in accordance with the present invention to known generator arrangements, such as that shown in FIG. 1, because to do so would be deemed to be prohibitively expensive because flow control mechanisms are expensive. However, the applicant has found that unexpectedly the advantages of the generator arrangement according to the present invention which are discussed below outweigh the significant additional cost of including a second flow control mechanism.

The provision of two flow control mechanisms within the present invention provides several advantages. The use of two flow control mechanisms allows the ratio of exhaust gas provided to each of the turbines 54 and 70 to be controlled. This allows the ratio of power produced by the turbocharger to that produced by the generator to be controlled more effectively than the prior art. For example, the use of two flow control mechanisms may provide a greater range of possible ratios or greater ability to accurately select a particular desired ratio.

Some embodiments of the generator arrangement according to the present invention may include an exhaust gas recirculation EGR path. Such an EGR path is indicated in dash lines in FIG. 2 and labelled 80. The EGR path 80 links the engine outlet 46 to the engine inlet 44. The EGR path 80 allows a portion of the engine exhaust gas to be recirculated to the engine inlet 44. This leads to a reduction in the temperature of combustion within the engine and hence a reduction in the amount of certain pollutants produces, for example the amount of nitrogen oxides produced. The EGR path may have a cooler (not shown) which cools the gas passing through it. The EGR path 80 also has an EGR control valve 82. The control valve 82 allows the EGR path 80 to be selectively opened and closed depending on the engine operating conditions.

In order for exhaust gas to flow from the engine outlet 46 to the engine inlet 44 via the EGR path 80, the EGR valve 82 will be at least partially open and there must be a pressure difference between the engine outlet 46 and engine inlet 44 such that the pressure of the exhaust gases in the engine outlet is greater than the pressure of the fluid (in this case air) in the engine inlet 44.

The provision of two flow control mechanisms within the generator arrangement in accordance with the present invention enables the amount of exhaust gas that is recirculated via an EGR path to be controlled. This is because the two fluid control mechanisms of the present invention allow both the flow passage for exhaust gas through the turbine of the turbocharger 48 and the flow passage for exhaust gas through the turbine of the generator 50 to be at least partially closed. At least partially closing at least one of (or both of) the flow passageways through both the turbines 54 and 70 will result in an increase in pressure of the exhaust gases in the engine outlet 46. This is because at least partially closing at least one of (or both of) the flow passageways through the turbines 54 and 70 will restrict the flow of the exhaust gases from the engine outlet to the arrangement outlet 68. By increasing the pressure of the exhaust gases in the engine outlet 46, the pressure difference between the gas in the engine outlet 46 and the fluid (in this case, air) in the engine inlet 44, and hence will increase the flow of exhaust gas from the engine outlet 46 to the engine inlet 44 via the EGR path 80.

The provision of two flow control mechanisms according to the present invention allows for greater control of the pressure within the engine outlet 46 and hence a greater control over the flow of exhaust gases from the engine outlet 46 to the engine inlet 44 via an EGR flow path. Furthermore, the provision of two flow control mechanisms in accordance with the present invention allows the flow of exhaust gas through the EGR path 80 to be controlled simultaneously whilst controlling the ratio of gas flow through the turbine 54 of the turbocharger 48, to that through the turbine 70 of the generator 50 (and hence controlling the ratio of power produced by the turbine 54 and the turbine 70).

FIG. 3 shows a generator arrangement 40a in accordance with a second embodiment of the present invention. Features of the generator arrangement 40a shown in FIG. 3 that are substantially the same as features of the generator arrangement shown in FIG. 2 have been given the same numbering.

The embodiment of the present invention shown in FIG. 3 differs from the embodiment shown in FIG. 2 in that the flow control mechanism of the turbine 70 of the generator 50 shown in FIG. 3 is a flow control valve 96 (as compared to a variable geometry mechanism as in the embodiment shown in FIG. 2). The flow control valve 96 may be actuated such that it is moveable between a fully closed position, in which essentially no exhaust gas can pass through it, and a fully open position, in which the flow control valve 96 may provide substantially no resistance to the passage of exhaust gas through it. The flow control valve 96 may be actuated such that it is placed in a state intermediate the fully open position and the fully closed position such that the flow control valve 96 partially inhibits the flow of exhaust gas through it. The flow control valve 96 may be actuated such that it is possible to choose a particular intermediate state of the flow control valve so that the flow control valve inhibits the flow of exhaust gas through it to a desired degree. In some embodiments, the flow control valve 96 may only move between an intermediate position and a fully open position or a fully closed position.

It will be appreciated that, although only the use of variable geometry mechanisms and flow control valves have been described in the role of flow control mechanisms, any appropriate flow control mechanism may be used. However, in some embodiments the use of variable geometry mechanisms may be advantageous because it allows a large degree of control over the amount of gas passing through and also the speed of the exhaust gas which reaches the turbine of which the variable geometry mechanism forms part.

It will also be appreciated that although the generator arrangements shown in both FIGS. 2 and 3 have a turbine 54 of the turbocharger 48 that is a variable geometry turbine, this need not be the case. For example, in some embodiments the turbine of the turbocharger may be a fixed geometry turbine.

Furthermore, the generator arrangement shown in FIG. 3 is such that the turbine 70 of the generator 50 is a fixed geometry turbine. This need not be the case. For example, the turbine of the generator may be a variable geometry turbine. That is to say, in some embodiments, the flow of gas to the turbine of the generator may be controlled by both a variable geometry mechanism which forms part of the turbine of the generator and a valve upstream of the variable geometry mechanism.

The turbine 54 of the turbocharger 48 shown in FIGS. 2 and 3 and the turbine 70 of the generator 50 both have an inducer portion upstream, in use, of the respective turbine wheel (not shown), and an exducer portion downstream, in use, of the respective turbine wheel. The exducer portion of each turbine may include a portion of the respective outlet of each turbine. The exducer portion of a turbine may be defined as the region of the turbine where the flow of gas which has passed the turbine wheel slows down and reduces its swirl rate. In addition, the cross-sectional flow area of the exducer portion may increase so as to defuse and slow down the gas flow.

The inducer portion of a turbine may be a region in which the flow rate of gas through the region increases. The cross-sectional flow area of the inducer portion may decrease so as to concentrate and increase the flow. The inducer portion may include at least a portion of the turbine inlet.

FIG. 4 shows a cross-sectional view through a portion of a generator arrangement 80 in accordance with an embodiment of the invention. The generator arrangement 80 of FIG. 4 shows an electric generator 84 and a turbine 82 of a turbocharger 83. As previously discussed, the electric generator 84 comprises a turbine 86 having a turbine wheel 88 which is linked by a shaft 90 to a transducer 92 (which in this case is an electric generator). The electric generator is of a known structural form whereby the electric generator comprises a rotor 94 which is linked to the shaft 90 and a stator 96. The rotor 94 and stator 96 are such that when the rotor rotates there is a relative motion between a magnetic field (not shown, produced by one of the rotor or the stator) and a coil (not shown, forming part of the other one of the rotor or the stator). The relative rotation between the magnetic field and coil results in electrical power being generated within the coil which can be extracted from the ends of the coil.

The shaft 90 of the generator 84 is supported by a bearing arrangement 98.

The turbine 86 of the generator 84 has a variable geometry mechanism 100 which comprises a sleeve 102 which is moveable relative to a fixed vane structure 104 so as to control the size of an axial inlet passageway 106. The axial inlet passageway 106 is surrounded by a generally volute-shaped inlet 108. The inlet passageway 106 is intermediate the inlet 108 and a turbine chamber 110 within which the turbine wheel 88 is located such that control of the size of the inlet passageway 106 controls the rate at which gas passes from the inlet 108 to the turbine chamber 110 via the inlet passageway 106.

Due to the fact that, in use, gas flows from the inlet 108 to the turbine chamber 110 via the inlet passageway in a direction which is generally radial with respect to the axis of rotation X-X of the turbine wheel 88 (and attached shaft 90) the turbine 86 of the generator 84 may be referred to as a radial inflow turbine.

The inlet 108 of the turbine 86 of the generator 84 forms part of an inducer portion of the turbine 86.

The turbine 82 of the turbocharger 83 of the generator arrangement 80 has an inlet volute 112 which is arranged around the turbine wheel (not shown) of the turbocharger. At a first end of the inlet volute 112 which is remote from the turbo wheel of the turbocharger 83, is a turbine inlet 114 via which exhaust gas from an engine outlet (now shown) is supplied to the inlet volute 112. The inlet volute 112 may be said to form part of the turbine of the turbocharger 83. Furthermore, an inducer portion of the turbine 82 of the turbocharger 83 may be said to include at least part of the inlet of the turbine 82 of the turbocharger 83. The inducer portion of the turbine 82 of the turbocharger 83 (which is located upstream of the turbine wheel of the turbocharger 83) comprises an inducer port 116.

The inducer port 116 is shown as a shaded portion within FIG. 4. The inducer port 116 is an opening which links the inducer portion of the turbine of the turbocharger 82 to the inducer portion of the turbine 86 of the generator 84. It follows that it may be said that the inducer port 116 is connected to the inducer portion of the turbine 86 of the generator 84. For example, the inlet volute 112 of the turbine of the turbocharger 82 may be connected to the inlet volute 108 of the turbine 86 of the generator 84 by the inducer port 116. It may also be said that, due to the inducer port 116 connecting the inlet volute 112 of the turbine of the turbocharger 82 and the inlet volute 108 of the turbine 86 of the generator 84, the inducer portion of the turbine of the turbocharger 82 and the inducer portion of the turbine 86 of the generator 84 are contiguous.

The turbine 86 of the generator 84 has an outlet 118. The outlet 118 is downstream, in use, of the turbine wheel 88 of the turbine 86. The outlet 118 extends in a direction which is generally parallel to the axis X-X of rotation of the turbine wheel 88. An exducer portion of the turbine 86 of the generator 84 may include at least part of the outlet 118.

The turbine of the turbocharger 82 also has an outlet 120 which is located downstream, in use, of the turbine wheel of the turbocharger 82. Within FIG. 4 the outlet 120 extends in a direction towards the reader perpendicular to the plane of the Figure. The turbine of the turbocharger 82 has an exducer portion which may include at least part of the outlet 120 of the turbine of the turbocharger 82.

The exducer portion of the turbine of the turbocharger 82 has an exducer port indicated generally as 122. The exducer port 122 is connected to the exducer portion of the turbine 86 of the generator 84. In particular, the exducer port 122 connects the outlet 120 of the turbine of the turbocharger 82 to the outlet 118 of the turbine 86 of the generator 84. In this way, gas which flows out of the outlet 118 of the turbine 86 of the generator 84 flows into the outlet 120 of the turbine of the turbocharger 82 and then out to atmosphere or an exhaust treatment system. Likewise, it may be said that gas from the exducer portion of the turbine 86 of the generator 84 flows via the exducer port 122 into the exducer portion of the turbine of the turbocharger 82.

The exducer port 122 is an opening which links the exducer portion of the turbine of the turbocharger 82 to the exducer portion of the turbine 86 of the generator 84. It follows that it may be said that the exducer port 122 is connected to the exducer portion of the turbine 86 of the generator 84. For example, the outlet 118 of the turbine 86 of the generator 84 may be connected to the outlet 120 of the turbine of the turbocharger 82 by the exducer port 122. It may also be said that, due to the exducer port 122 connecting the outlet 118 of the turbine 86 of the generator 84 and the outlet 120 of the turbine of the turbocharger 82, the exducer portion of the turbine of the turbocharger 82 and the exducer portion of the turbine 86 of the generator 84 are contiguous.

The turbine wheel of the turbocharger 82 rotates about an axis indicated by Y which extends perpendicular to the plane of the Figure. It can be seen that in the embodiment of the invention shown in FIG. 4, the generator 84 is arranged relative to the turbocharger 82 such that the axis of rotation (X-X) of the turbine wheel 88 of the turbine 86 is perpendicular to the axis (Y) of rotation of the turbine wheel of the turbine of the turbocharger 82. In some applications, arranging the generator and turbocharger such that the axis of rotation of the turbine of the generator and the axis of rotation of the turbine of the turbocharger are perpendicular to one other may be disadvantageous. This is because arranging the turbocharger and the generator in this manner means that the inducer and/or exducer port(s) are such that there is a substantially perpendicular flow of the gas through the respective port relative to the general direction of the gas flow within the inducer portion or exducer portion of the turbine of the turbocharger. This flow of gas through substantially a right angle may be disadvantageous in some applications due to the fact that it may cause undesirable turbulence in the flow of the gas and/or an undesirable reduction in the flow speed of the gas through the port. This may lead to a reduction in the performance of the generator and/or turbocharger.

The angle between the general flow of gas through a port and the general direction of flow of gas through the inducer or exducer portion of the turbine of the turbocharger of which the port forms part may be referred to as a take-off angle. Consequently, the ports shown in the arrangement of FIG. 4 have a take-off angle which is approximately 90°. In some embodiments of the present invention it is preferable that the take-off angle of any port linking a pair of inducers or exducers is less than about 45°. Even more desirably, the take-off angle between a pair of exducers or inducers may be less than at least one of about 30°, about 20°, about 10° and about 5°.

Another way of describing the take-off angle is the angle subtended between the general flow direction of fluid within a portion of a first inducer portion (for example the inducer portion of the turbine of the turbocharger) upstream of the inducer port, and the general flow direction of fluid within a portion of the second inducer portion (for example the inducer portion of the turbine of the generator) downstream of the inducer port. Likewise, the take off angle may be defined as the angle subtended between the general flow direction of fluid within a portion of a second exducer portion (for example the exducer portion of the turbine of the generator) upstream of the exducer port, and the general flow direction of fluid within a portion of a first exducer portion (for example the exducer portion of the turbine of the turbocharger) downstream of the exducer port. As previously discussed, in some embodiments of the present invention it is preferable that the take-off angle of any port linking a pair of inducers or exducers is less than about 45°. Even more desirably, the take-off angle between a pair of exducers or inducers may be less than at least one of about 30°, about 20°, about 10° and about 5°.

FIG. 5 shows a turbine 150 of turbocharger and a turbine 152 of a generator arrangement 154 in accordance with an alternative embodiment of the present invention. In this embodiment, the turbine wheel (not shown) of the turbine 152 of the generator rotates about an axis indicated by X which extends generally perpendicular to the plane of the Figure. The turbine wheel (not shown) of the turbine 150 of the turbocharger rotates about an axis indicated by Y which also extends in a direction which is generally perpendicular to the plane of the Figure. Consequently, it can be seen that the axis of rotation X of the turbine 152 of the generator is substantially parallel to the axis of rotation Y of the turbine wheel of the turbocharger 150.

The turbine 152 of the generator incorporates a variable geometry mechanism (not shown). The variable geometry mechanism operates in the same manner as the variable geometry mechanism described in relation to FIG. 4 and includes a moveable sleeve which is indicated by the dotted line 156.

Not only are the axes of rotation (X, Y) of the turbine wheels substantially parallel to one another, but also the inlets of the turbines and the outlets of the turbines are arranged such that they are generally parallel to one another. This is beneficial in some embodiments of the invention because if the inducer portions and/or exducer portions of the turbine of the generator and the turbine of the turbocharger are parallel, then it may be possible to arrange the inducer portions and/or exducer portions such that they are contiguous without the need for a port which has a large take-off angle. This can be seen in the embodiment shown in FIG. 5 as discussed below.

The turbocharger 150 of the generator arrangement 154 shown in FIG. 5 has an outlet 158. The turbine 152 of the generator of the generator arrangement 154 has an outlet 160. A gas passageway 162 (which may be referred to as a port) extends between the outlet 158 and the outlet 160. The gas passageway 162 extends in a direction which is substantially parallel to the axes X and Y such that the gas passageway 162 extends parallel to the outlets 158 and 160. In this way, the exducer portions of the turbine 150 and turbine 152 (which include the outlets 158 and 160 respectively) are contiguous and gas from the outlet 160 (and hence the exducer portion of turbine 152) can mix with gas from the outlet 158 (and hence exducer portion of the turbine 150) without the need for the gas from the outlet 160 to flow along a tortuous path to the outlet 158 of the turbine 150. In this context, a tortuous path refers to a path between the exducer portion of the turbine 152 and the exducer portion of the turbine 150 which includes at least one turn which is sufficiently sharp so as to significantly reduce the speed of gas flow between the exducer of the turbine of the generator and the exducer portion of the turbine of the turbocharger, and/or so as to significantly increase the turbulence in the gas flow between the exducer of the turbine of the generator and the exducer of the turbine of the turbocharger.

It will be appreciated that by ensuring the flow path between the exducer portion of the turbine of the generator and the exducer portion of the turbine of the turbocharger is such that the speed of gas flow between the two is maximised and the amount of turbulence in the flow between the two is minimised, then the performance of the generator and the turbocharger is maximised.

FIG. 6 shows the turbines of a turbocharger 150 and generator 152 of a generator arrangement 154 in accordance with a further embodiment of the present invention. The schematic layout of this embodiment is shown in FIG. 3. However, the turbine 54 of the turbocharger 48 shown in FIG. 3 is of a variable geometry type, whereas the turbine of the turbocharger 150 shown in FIG. 6 is of a fixed geometry type. The generator arrangement 154 includes a flap valve 170. The flap valve 170 is located upstream of an inducer portion of the turbine 152 of the generator. The flap valve includes a flap member 172 which is moveable between an open position (as shown in FIG. 6) and a closed position (not shown). The flap valve also includes an opening 174 which links an inducer portion of the turbine 152 of the generator and an exhaust outlet of the engine (not shown). In some cases, the opening may link an exducer portion of the turbine 152 of the generator with a portion of an inlet of the turbine 150 of the turbocharger (the inlet of the turbine of the turbocharger may form part of an inducer portion of the turbine 150 of the turbocharger). In this case, the inlet of the turbine 150 of the turbocharger is connected to an outlet of the engine such that gas from the engine outlet can pass into the inlet of the turbine 150 of the turbocharger. Gas can then pass from the inlet of the turbine 150 of the turbocharger via the opening 174 to an inducer portion of the turbine 152 of the generator.

When the flap member 172 is in the open position, the flow of gas through the opening 174 is substantially unimpeded by the flap member. Consequently, when the flap member 172 of the flap valve 170 is in the open position, exhaust gas can flow through the opening from the inducer portion of the turbine of the turbocharger to the inducer portion of the turbine of the generator 152. When the flap member 172 of the flap valve 170 is in the closed position, the flap member 172 substantially blocks the opening 174 such that the flow of gas between the exhaust outlet of the engine and the inducer portion of the turbine 152 of the generator via the opening 174 is substantially prevented, i.e. exhaust gas substantially cannot flow through the opening from the inducer portion of the turbine of the turbocharger to the inducer portion of the turbine of the generator 152. It will be appreciated that when the flow of gas between the engine outlet and the inducer portion of the turbine 152 of the generator is substantially prevented, the generator does not generate any power.

In the embodiments of the invention shown in FIGS. 4, 5 and 6, the generator arrangement in each case has a housing which defines at least a portion of a turbine housing of the turbocharger and at least a portion of the turbine housing of the generator. In the embodiments shown in FIGS. 4, 5 and 6, the entire turbine housing of the turbocharger and the entire turbine housing of the turbine of the generator are defined by a single housing of the generator arrangement. In this case, the housing of the generator arrangement defines the inducer portion, the exducer portion and the turbine chamber of the turbine of the turbocharger. The turbine chamber of the turbine of the turbocharger is a chamber within which the turbine wheel of the turbine of the turbocharger is located (and within which, in use, the turbine wheel of the turbine of the turbocharger rotates). Furthermore, the housing of the generator arrangement defines the exducer portion, inducer portion and a turbine chamber of the turbine of the generator. The turbine chamber of the turbine of the generator is a chamber within which the turbine wheel of the turbine of the generator is located (and within which, in use, the turbine wheel of the turbine of the generator rotates).

In other embodiments of the present invention, the housing of the generator arrangement defines a portion of the housing of the turbine of the turbocharger and a portion of the housing of the turbine of the generator. The portion of the turbine of the turbocharger which is defined by the housing of the generator arrangement may include at least part of the exducer portion of the turbine of the turbocharger, at least part of the inducer portion of the turbine of the turbocharger and/or at least part of the turbine chamber of the turbine of the turbocharger. Similarly, in some embodiments of the invention, the portion of the turbine housing of the turbine of the generator which is defined by the housing of the generator arrangement may include at least part of the exducer portion of the turbine of the generator, at least part of the inducer portion of the turbine of the generator and/or at least part of the turbine chamber of the turbine of the generator.

In the embodiments shown in FIGS. 4 to 6 the housing of the generator arrangement which defines the turbine housing of the turbine of the turbocharger and the turbine housing of the turbine of the generator is of unitary construction. However, in other embodiments of the present invention this may not be to the case.

FIG. 7 shows an end-on view of a turbine 180 of a turbocharger and a turbine 182 of a generator which form part of a generator arrangement 184 in accordance with an embodiment of the present invention. In common with the embodiments of the invention shown in FIGS. 5 and 6, the embodiment of the invention shown in FIG. 7 is such that the axis of rotation of the turbine wheel (not shown) of the turbine 180 is substantially parallel to the axis rotation (X) of the turbine wheel (not shown) of the turbine 182 of the generator.

In contrast to the embodiments shown in FIGS. 4 to 6, the turbine 180 of the turbocharger and the turbine 182 of the generator have separate housing (186 and 188 respectively). The housing 188 which defines the turbine 182 of the generator, further defines an inlet portion 190. The inlet portion 190 has an inlet 192 which is supplied, in use, with exhaust gas from an engine outlet. The inlet portion 190 further comprises a port 194 which allows gas from the inlet 192 to flow into an inducer portion (and, in particular, into an inlet volute 196) of the turbine 182. The inlet portion also has an outlet 198 which is connected to an inlet 200 of the turbine 180. Consequently exhaust gas from the engine outlet can flow from the inlet 192 of the inlet portion 190 to the outlet 198 of the inlet portion 190, and then into the inlet 200 of the turbine 180. The exhaust gas flowing into the inlet 200 of the turbine 180 flows into an inducer portion (and, in particular, an inlet volute 202) of the turbine 180.

As before, the turbines 180, 182 each have a respective outlet 210, 212. These outlets 210, 212 although not linked by the housings 186 and 188 of the respective turbines 180, 182, may be linked at a location (not shown) downstream of the outlets 210, 212 such that they pass to a common outlet of the engine to which they are attached or a common exhaust gas treatment assembly.

The dotted line 204 indicates the presence of a moveable sleeve within the turbine 182 of the generator which forms part of a variable geometry mechanism.

The operation of the variable geometry mechanism in this case will not be discussed because the variable geometry mechanism operates in the same way as that of the previously described embodiment.

The turbine 180 of the turbocharger and turbine 182 of the generator are secured to one another such that the outlet 198 of the inlet portion 190 and the inlet 200 are connected. This attachment may be achieved by securing a flange 206 of the turbine 180 and a flange 208 of the turbine 182 together.

It will be appreciated that although the turbine 180 and the turbine 182 have separate housings 186, 188, the housings 186 and 188 may be said to form a single housing comprising two separate pieces. It will also be appreciated that the inlet portion 190 of the turbine 182 may be said to form part of the inducer portion of the turbine 180 of the turbocharger. In this way, it can be said that the inducer portion of the turbine 180 of the turbocharger and the inducer portion of the turbine 182 of the generator are contiguous because the inducer portion of the turbine 180 of the turbocharger and the inducer portion of the turbine 182 of the generator are connected to one another by the inlet portion 190 and the port 194.

Although some of the embodiments of the present invention shown above are such that the axes of rotation of the turbine wheels of the turbocharger turbine and generator turbine are substantially parallel, in other embodiments this need not be the case. For example, in some embodiments there may be a slight angle between the axes of rotation of the turbine wheels. For example, the axes of the turbine wheels may be arranged such that they generally converge in a direction such that the respective outlets of the turbine of the turbocharger and the turbine of the generator also converge. In this way, the generator arrangement (and hence a housing of the generator arrangement) may be arranged such that the respective outlets of the turbine of the turbocharger and the turbine of the generator converge to a single outlet. Consequently, the exhaust gases from each of the turbocharger turbine and generator turbine can both flow out though the single outlet.

Other possible modifications and applications of the invention will be readily apparent to the appropriately skilled person. 

1. A generator arrangement comprising: a turbocharger having a compressor configured to be placed in fluid flow communication with an engine inlet, and a first turbine having a first turbine wheel, a first inducer portion upstream, in use, of the first turbine wheel and configured to be placed in fluid flow communication with an engine outlet, and a first exducer portion downstream, in use, of the first turbine wheel; and an electrical generator having a second turbine having a second turbine wheel, a second inducer portion upstream, in use, of the second turbine wheel and configured to be placed in fluid flow communication with the engine outlet, and a second exducer portion downstream, in use, of the second turbine wheel; wherein the first and second turbines are arranged in parallel to one another; and wherein the first inducer portion and second inducer portion, and/or the first exducer portion and second exducer portion are contiguous.
 2. A generator arrangement according to claim 1, wherein the generator arrangement comprises a housing which defines at least a portion of a first turbine housing of the first turbine and at least portion of a second turbine housing of the second turbine, wherein the portion of the of the first turbine housing defines at least part of the first exducer portion, at least part of the first inducer portion or at least part of a first turbine chamber within which the first turbine wheel is located, and wherein the portion of the of the second turbine housing defines at least part of the second exducer portion, at least part the second inducer portion or at least part of a second turbine chamber within which the second turbine wheel is located.
 3. A generator according to claim 2, wherein the housing is of unitary construction.
 4. A generator arrangement according to claim 1, wherein the second turbine is a radial inflow turbine.
 5. A generator arrangement according to claim 1, wherein the first turbine and/or second turbine are variable geometry turbines.
 6. A generator arrangement according to claim 1, wherein the second turbine comprises a flow control device which is configured to control the flow of fluid from the engine outlet to the second turbine.
 7. A generator arrangement according to claim 6, wherein the flow control device is a valve.
 8. A generator arrangement according to claim 1, wherein the first turbine wheel, in use, rotates about a first axis, and the second turbine wheel, in use, rotates about a second axis, the first and second axes being substantially parallel.
 9. A generator arrangement according to claim 1, wherein the first inducer portion comprises an inducer port to which the second inducer portion is connected, and/or wherein the first exducer portion comprises a exducer port to which the second exducer portion is connected.
 10. A generator arrangement according to claim 9, wherein, the first inducer portion comprises an inducer port to which the second inducer portion is connected, and wherein, in use, the angle subtended between the general flow direction of fluid within a portion of the first inducer portion upstream of the inducer port and the general flow direction of fluid within a portion of the second inducer portion downstream of the inducer port is less than about 90 degrees.
 11. A generator arrangement according to claim 9, wherein, the first exducer portion comprises an exducer port to which the second exducer portion is connected, and wherein, in use, the angle subtended between the general flow direction of fluid within a portion of the second exducer portion upstream of the exducer port and the general flow direction of fluid within a portion of the first exducer portion downstream of the exducer port is less than about 90 degrees. 